Q: I just maxed out my 512Mb CF at 157 images though the guide says 198. Why?
A: This can happens if your pictures have a lot of detail in them. Try to take pictures of blue skies and probably you will end with more than 200 pictures in your CF. This is because when the image has less detail, JPEG compression is more efficient reducing data. The guide figures are only indicative (as the "remaining pictures" counter in your camera) and they are calculated using a mix of high and low detailed pictures, but usually "real word" numbers are somewhat lower.